Justice Anthony M. Kennedy, often considered a swing vote, joined the majority, tipping the decision to the conservative side of the court.

The more liberal justices sided with the Longs in upholding tribal court jurisdiction. In her dissent, Justice Ruth Bader Ginsburg disagreed with the characterization of the case as one over fee land.

"Resolving this case on a ground neither argued nor addressed below, the court holds that a tribe may not impose any regulation -- not even a nondiscrimination requirement -- on a bank's dealings with tribal members regarding on-reservation fee lands," Ginsburg wrote.

But even if the case were about the sale of fee land, Ginsburg said tribal courts are the proper place to resolve a dispute involving a non-Indian bank that voluntarily entered into a business agreement with tribal members. "Sales of land -- and related conduct -- are surely 'activities' within the ordinary sense of the word," she wrote, citing some of the same precedents that Roberts relied on.

The decision means the Longs are not entitled to a $750,000 jury verdict awarded by a Cheyenne River Sioux court. With interest, the judgment would have to about $870,000.

The case was Alito's first Indian law case since he joined the court in February 2006. He previously served as a judge for the 3rd Circuit Court of Appeals, where there are no federally recognized tribes.